Institute of Electrical and Electronics Engineers (IEEE) standards publications 802.11 outline protocols for implementing wireless local area networks (WLAN). IEEE 802.11 sets forth a physical (PHY) layer frame format that includes a preamble composed of three fields, namely, a short training field (STF), a long training field (LTF), and a signal (SIG) field. The STF is used for packet detection, automatic gain control (AGC), and coarse synchronization, the LTF is used for channel estimation and fine synchronization, and the SIG field specifies parameters of the frame (e.g., frame rate, frame length, etc.). IEEE 802.11ac (2012) is a communication standard for providing high-throughput in wireless local area networks (LANs), and is incorporated herein by reference as if reproduced in its entirety.
Channel equalization is performed to remove distortions from a received frame, and relies on the accurate channel estimation. The channel estimation is performed to estimate conditions of the air channel, and relies on analyzing the received LTF. In IEEE 802.11ac networks, the SIG field is typically interleaved prior to transmission, while the LTF/STF preamble fields are typically transmitted without interleaving. Non-linear channel equalization technique must generally be performed concurrently with channel decoding, whereas the conventional IEEE 802.11 networks are typically limited to linear equalization (e.g., zero-forcing equalization), which may generally be less effective at removing distortion from the signal than non-linear channel equalization techniques (e.g., maximum likelihood equalization, etc.).
IEEE standards publication 802.11ah is a planned derivative of IEEE 802.11ac that is expected to be released in 2015, and will be specifically tailored for sensor network, data off-loading, and smart metering applications. While IEEE 802.11ah will share many similarities with IEEE 802.11ac, modifications to various IEEE 802.11ac protocols are desired to allow IEEE 802.11ah networks to better serve sensor networks, data-offloading, and smart metering applications.